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  • Cabinet assembly question

    Hello everyone, one question, I went with ¾” sides, top/bott (dado into the sides) and ¾” backs (rabbetted in), face frames on the front. I plan on gluing all parts and also using a mechanical attachment if needed. Should I use brads, nails or screws? For the back should I put the fastener in from the sides or rear? Even though they are for the shop I’d like them to look as good as possible. Maybe I’m over analyzing this but I want to do right the first time. Thanks for your replies Pat
    Last edited by PMR413; 05-27-2010, 07:19 PM.

  • #2
    Re: Cabinet assembly question

    I use glue and lots of clamps until the glue cures, on the back panel, when it will not be visible, I use glue and brads (from the rear) instead of clamps. If the top of the Cabinet had a counter, then that's where the screws would come into play.

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    • #3
      Re: Cabinet assembly question

      I agree, just be sure to keep the cabinets square when applying clamping pressure. Very little pressure is required with good joints, basically just enough to see some glue squeeze out. One mistake that is common is to over tighten the clamps thereby squeezing the majority of the glue out which weakens the joint

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      • #4
        Re: Cabinet assembly question

        Hi Pat,

        Is your project a wall mount or a base cabinet? It makes a difference as to the best way to go.

        If it's a base cabinet, then glue and either nail or screw the backs on, it makes little difference which. Install the screws or brads from the back. I tend to prefer screws over nails but either will be fine. If I had a brad nailer I would probably prefer to use it to save time.

        If it's a wall cabinet, that's different. Your cab will be hung on the wall through the back, so you need a very good lock between the back and sides. Drive the screws in from the side. Your sides will then be locked to the back by the screws, loaded in shear. For a wall cab, this is far stronger than putting the screws in from the back, which are subject to pulling out. With your 3/4 material, there is plenty of thickness there to let you counterbore and install plugs to hide the screws if you want. Or, if you want to get fancy you can rout a groove and inlay a strip to cover the screwheads, then scrape it flush. It can be invisible if done carefully.

        For wall cabs especially, I do not rely on the glue to hold the cabinet to the back. Wood glue is great stuff, but a ply edge is always about 50% end grain - and gluing end grain is iffy at best. You don't want your structure totally dependent on an end-grain glue join for a wall-mounted cabinet, attached through the back. Hence the recommendation above to drive the screws in from the sides.

        For wall mount cabs, I have found that a VERY strong construction method is to dado the sides, top and bottom so that the back is captured in dados on 4 sides. With this construction, which is a little bit more time consuming and exacting, the back is fixed to the wall, and the sides, top and bottom are mechanically locked to the back. The cabinet will NEVER come down. There is no need for any metal fasteners with this construction - it's rock solid.

        Glue only should be plenty strong enough for the rest of the carcass since you have dados, as long as they fit fairly well. You can use brads to clamp the glue joints if you don't have enough clamps, and then use one strategically applied clamp to get the carcass perfectly square if needed.

        I FULLY second the comment about not over-clamping. You need to make sure there is a good amount of glue in your joints! If your having to over-tighten the clamps, it means that things aren't fitting properly. Pulling poor fitting joints together by tightening the clamps is a common mistake. The cabinet will seem fine but is very likely to develop problems down the road.

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        • #5
          Re: Cabinet assembly question

          Nails are the strongest. Screws are best if used with glue, as you can use ones that are coated to resist corrosion [yes, wood glue (pva type like titebond or elmers) corrodes steel. Just drop some on you saw table top if you don't believe it). Brads are only good for temporary holding. They will corrode out and have little structural strength.

          Andy's advise about wall cabinet joinery is spot on. The stretcher or back is screwed to the wall. The top (extending over the stretcher if used) supports the sides via the dado joints. The sides support all the shelves and bottom through dado joints. This means the top and bottom are dadoed into the sides, not rabbeted, I currently have five made like this holding well over 300 lbs each that have been on my garage wall for several years. I used the "french cleat" method of hanging (no screws into the wall, but the top extends back over the cleat). The 3/4" thick shelves are adjustable using 1/4" normal shelf pins. As I used a 3/4" back, I also put a dual row of pins in the back to help the heavier shelf weights.

          Go
          Practicing at practical wood working

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          • #6
            Re: Cabinet assembly question

            Nails are the strongest. Screws are best if used with glue....
            Is this correct or are you testing to see if anyone is paying attention?

            I think screws make a stronger connection than nails alone. Nails and
            glue would be second to screws with glue to my way of thinking.
            "It's a table saw, do you know where your fingers are?" Bob D. 2006

            https://www.youtube.com/user/PowerToolInstitute

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            • #7
              Re: Cabinet assembly question

              I prefer screws, and if you want the screws hidden the Kreg jig is great for that,

              I pre drill the screws or at lest starter or pilot holes,

              all I know is if using a air nailer, and it curls the nail or brad it is a mess getting it out of the way and pulled,

              on your bottom to the sides, (even with dado) one can use a cleat and screw both ways into the bottom and into the sides, (cleat on the bottom of the bottom board),
              Push sticks/blocks Save Fingers
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              • #8
                Re: Cabinet assembly question

                The only point at which screws are weaker is in shear strength, otherwise for straight holding strength, they are superior. There are nails that are threaded or barbed which can make them hold better but all things being equal, a screw is a better tool for the job.

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                • #9
                  Re: Cabinet assembly question

                  Bob D.:

                  The statement about nails being strongest was in reference to shear strength. For a wall hanging cabinet, shear strength may be the major factor, but it is still dependent on the joint design. Nails are softer steel, but tougher when it comes to breaking (they will distort long before they break). Most of todays screws are made with a shank diameter smaller than the outside thread diameter, giving a weak point. They are also hardened somewhat to resist the heads rounding out. However, the hardness also makes them more brittle. The older style wood screws (most with slot heads), are probably as strong or stronger than nails, as the shank is full size of the max thread OD, and most were not hardened. For pull strength in a cabinet, nails, especially pin or wire nails, aren't much better than brads. Drywall screws are the worst, as they will readily corrode and are very brittle. The do work well to hold a glue up in place if they are removed after the glue sets, and the holes filled.

                  In softer woods, like construction pine, my experience has been that cement coated nails are harder to remove than screws. Ring shanks are about equal. I do not have any scientific data to base this on, just personal experience, so please accept my apologies for not stating "IMHO". This does not apply in decks, treated and wet lumber, because the wood is too soft for ring shanks to get a good hold, and too wet for the friction of driving them in to activate the cement coating. The over-sized threads on deck screws and the deep threads of lag bolts are much better in that environment.

                  That said: IMHO, for cabinets, the reality is that with proper joinery, the glue is the biggest factor. The screws aid in the construction, and are critical when hanging, but in the cabinet itself, a snug well glued joint that is perpendicular to the major stress direction most likely does not need the screws after the glue dries. They do give a little back-up to let you know if the glue fails, and a chance to repair it before catastrophic failure.

                  JMTCW and the above is my opinion based on my experience.

                  Go
                  Last edited by Gofor; 06-04-2010, 08:43 PM.
                  Practicing at practical wood working

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                  • #10
                    Re: Cabinet assembly question

                    I pref-are to use screws just make sure they are hidden

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                    • #11
                      Re: Cabinet assembly question

                      I avoid using fasteners to carry load... but on rare occasion when I have to (always in shear, never in tension), I prefer screws. I like the Deckmate coated deck screws with good results. I especially like that these have pozi heads instead of phillips - much better! I pre-drill and countersink for the heads, or if visible go under-flush and use plugs or an inlaid strip.

                      You can usually use a larger screw that the nail you would select, so the screw can be stronger in shear than the nail. I don't worry too much about the brittleness - if the fastener starts to plastically deform in shear, the battle is lost anyway. But I never use drywall screws in anything except drywall because of the corrosion. Even in non-structural applications, they will turn your wood black and ruin the piece. It's a sad lesson to have learned.

                      Again, proper design with no metal fasteners is by far the strongest and most trouble free for wall cabinets. I do now have a brad nailer and have used brads to clamp. But clamps, if you have them, are still better because there are no holes to fill and no brads to corrode.

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                      • #12
                        Re: Cabinet assembly question

                        Agree re Pozidrive screws. Sadly they are well behind Philips in popularity in the US. It's a shame, they are vastly superior screws. As common as the drywall screw is in the US, bright zinc plated pozidrive screws are in Europe. I try and buy a box every time I visit, although they are heavy!

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                        • #13
                          Re: Cabinet assembly question

                          Correct me if I am wrong but the only properties that matter when it comes to shear strength is material (steel, brass, etc) and cross sectional area or diameter of the nail or screw.

                          So if a properly sized screw is selected then it should be equal to a nail of the same diameter given the same material. For a screw that would mean selection would consider the minor diameter of the shank. If the minor dia. is equal the nail diameter how can they not develop the same shear?

                          What am I missing?
                          "It's a table saw, do you know where your fingers are?" Bob D. 2006

                          https://www.youtube.com/user/PowerToolInstitute

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                          • #14
                            Re: Cabinet assembly question

                            Originally posted by Bob D. View Post
                            Correct me if I am wrong but the only properties that matter when it comes to shear strength is material (steel, brass, etc) and cross sectional area or diameter of the nail or screw.

                            So if a properly sized screw is selected then it should be equal to a nail of the same diameter given the same material. For a screw that would mean selection would consider the minor diameter of the shank. If the minor dia. is equal the nail diameter how can they not develop the same shear?

                            What am I missing?
                            You're not missing much, but there are some fine points you might find interesting, albeit information overkill.

                            The material consideration needs to include the specific properties of the alloy and the heat treatment. Screws are often heat treated so the heads won't strip as easily (as we all know, some are not). Heat treatment imparts hardness and an increase in yield and ultimate strength, at the expense of ductility (i.e., increased brittleness).

                            Diameter and area are of course related, so they are really the same thing. Except that with a screw, you have three areas... one based on major diameter, one based on minor diameter and the "stress area", which basically accounts for the material that is in the thread when you take a cross section. The stress area will be greater than that computed considering only the minor diameter. So if you base your selection on the minor diameter, you'll be safe... engineers generally use the stress area in bolt calculations, but then again they generally have much better information on the level of loading and are doing a little more involved analysis.

                            A nail is actually more likely to be loaded predominately in shear than a screw. This is because the nail is driven through both pieces, so that both parts fit tight tot he nail. Screws in wood working are most often installed by drilling a clearance hole in one part (the one with the head of course) and screwing into the second part (with or without a pilot hole). The clearance hole is generally needed so that the parts will draw up tight when the screw is installed. But, because of the clearance hole, when the joint is loaded in shear, load is transferred to the screw through the screw head. This means that the screw is seeing predominately bending, not shear. Complicating things further is the flat head most often used in woodworking. The load applied at the head thus also increases the axial (tension) applied to the screw. So, the entire state of stress in a screw becomes pretty complicated. And there's a lot more going on than I've mentioned above. But even in a nail, when you put the joint under high shear loads, the wood tends to wallow out and so even a nail is actually not seeing pure shear... although in many cases it's closer than a screw.

                            But all that doesn't really matter. After all, we're not building the space shuttle, and who actually performs stress analysis on a cabinet? We all just pick screws or nails that feel right, so a deep understanding of the topic is really just of academic interest.

                            Bottom line, if you're building a wood project that will be lightly loaded, metal fasteners are probably ok. If it's going to see some substantial loading (as in the case of a wall hung cabinet), then screws or nails aren't a great choice. With either, the loads have to essentially neck down to pass through the nail or screw. You can combat this by using a lot of fasteners (think of riveted airplane structures), but with wood, you're most often much better advised to design the box and mounting system with joinery so that the loads are spread out and avoid the whole problem.

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